Catechism of the Catholic Church
691 "Holy Spirit" is the proper name of the one whom we adore and glorify with the Father and the Son. The Church has received this name from the Lord and professes it in the Baptism of her new children. 16
The term "Spirit" translates the Hebrew word ruah, which, in its primary sense, means breath, air, wind. Jesus indeed uses the sensory image of the wind to suggest to Nicodemus the transcendent newness of him who is personally God's breath, the divine Spirit. 17 On the other hand, "Spirit" and "Holy" are divine attributes common to the three divine persons. By joining the two terms, Scripture, liturgy, and theological language designate the inexpressible person of the Holy Spirit, without any possible equivocation with other uses of the terms "spirit" and "holy."
English Translation of the Cathechism of the Catholic Church for the United States of America © 1997, United States Catholic Conference, Inc.